Infusion systems, including intravenous (IV) delivery of fluids and drugs, have been used for nearly 200 years. Today, infusion systems remain a fundamental and integral part of the routine care of patients, especially those undergoing chemotherapy, anesthesia, blood transfusions, insulin therapy, and fluid or electrolyte replacement. Systems to control the subcutaneous or even transdermal delivery of therapeutic agents are also commonly used, particularly to manage chronic pain, for example. However, inappropriate IV therapy remains a significant cause of patient morbidity and mortality most commonly resulting from administration of an incorrect volume (e.g. over or under delivery of the desired drug dosage) and/or administration of an incorrect fluid or drug. Drugs are delivered to the site of action extremely rapidly with IV injection and the effects are often experienced in as little as 10 seconds after dosing. Thus, there is a high risk of overdose if the dose has been calculated incorrectly. There is also an increased risk of deleterious side effects if the drug is administered too rapidly.
During administration, invariably there is a need for dosing therapeutic agents at constant and/or predetermined flow rates. In addition to providing a basal infusion rate (i.e. maintenance IV fluids), it is desirable that these medications are carried into the cannulated vein by a continuous IV flow. Administration of excess quantities of IV fluids is wasteful, undesirable and often harmful to the patient causing conditions such as edema. In addition to the above, the need to mix therapeutic agents with an IV solution invites human error including the potential to provide an incorrect mixture of drugs and/or an incorrect dosage of drugs to the patient. This is particularly the case during various surgical and/or emergency medical procedures where there is often a need to quickly administer various drugs and/or IV fluids.
The most commonly used IV infusion system consists of a bag filled with fluids, a drip chamber, roller clamp (i.e. variable resistance controller) for control of the flow and tubing connected to an IV catheter. The elevated IV bag in this system serves as a pressure source, the roller clamp as a user-controlled resistor, and the IV catheter as a fixed resistor.
Most commonly, the rate of IV fluids flow is determined by the rate at which drops of liquid are observed falling through a drip chamber. A miscalculation of flow rate can lead to many problems including extravasation, infusion phlebitis, infiltration, and even death. Gravity infusion of the parenteral solution is accomplished by suspending the solution container several feet above the patient and connecting the solution container to the venipuncture site via a disposable intravenous administration set which includes a drip chamber and flexible delivery tube.
Intravenous flow rates, usually expressed in: 1) number of drops; 2) cubic centimeters per minute (cc/min); or 3) milliliters per minute (ml/min), are commonly controlled by use of a roller clamp. U.S. Pat. No. 4,175,558 describes a roller clamp for collapsing the delivery tube to control the flow rate. The roller clamp is a simple, inexpensive, two-piece plastic device that progressively compresses the plastic tube of the intravenous administration set at a single point on the tube thereby occluding the tube to create a pressure drop across the restriction and a corresponding reduction in flow rate. The constancy of flow rates during use of such roller clamps is problematic due to cold flow or creep of the plastic tubing at the point of restriction, which causes the flow rate to decrease after setting. Another drawback is that the roller clamp requires electricity or battery power to function.
Continuous flow through the infusion system is usually necessary to ensure the proper delivery of the injected drugs into the patient and avoid accumulation of repeated doses within the IV tubing. However, administration of excess IV fluids is undesirable and frequently harmful. Even in otherwise healthy patients, inadvertently administered large volumes of IV fluids can result in urinary bladder distention and need for urethral catheterization during the surgery, or urinary obstruction post-operatively, all of which can cause increased hospital stays for the patient. In patients with heart or lung disease, the administration of excessive fluid volumes is a frequent cause of postoperative lung and cardiovascular dysfunction. This can result in congestive heart failure, pulmonary edema (i.e. swelling of the lungs) and difficulties in discontinuing mechanical ventilation (i.e. breathing machine) after surgery and anesthesia.
Historically, infusion systems can be difficult to control and the flow rate is cumbersome and inexact. Since these systems are capable of delivering high flow rates, failure to frequently assess and adjust the infusion rate using a roller clamp can easily result in administration of excess IV fluids. The risk of administering large fluid volumes is ever present also due to the deficiencies inherent in these infusion systems. For instance, the rate of drip formation has been found to be an inaccurate measure of flow rate because of the influence of temperature, fluid composition, orifice diameter, and orifice shape. Furthermore, the cold flow (i.e. “creep”) in the tubing underlying the roller clamp can contribute to flow variation in excess of 15% over 45 minutes. When a vein collapses, critically high flow velocities occur, causing the distention of the vessels (produced by the downstream resistance) and paradoxically increase in the IV flow.
Veins are characterized by an opening pressure and by a small resistance to flow. Tissues behave as ordinary resistors with a resistance higher than that of veins. The opening pressure of tissue usually is no greater than that of veins, at least initially. In tissues, there is no obstructing pressure when there is no extravasation. However, as fluid is infused, opening tissue pressure rises. In response to these changes in flow rates, the clinician frequently has to check and adjust the roller clamp in order to properly adjust the IV flow so that the flow is continuous, keeping the veins open and assuring the delivery of administered medications and anesthetics, but not excessive to result in fluid overload or infusion of inappropriately large quantities of IV fluids.
Systems for administering intravenous liquids are described in U.S. Pat. Nos. 3,298,367 and 5,318,515. These patents generally describe a plurality of separate flow paths with each flow path having various flow characteristics. During operation and delivery of IV fluids both these patents would require a time consuming selection from a finite number of tubes and associated flow characteristics. Several flow rate regulators, including U.S. Pat. Nos. 3,877,428 and 5,019,055, have been introduced in recent years in attempts to overcome the aforementioned disadvantages associated with the use of conventional roller clamps and infusion procedures.
Information related to attempts to address these or similar problems can be found in U.S. Pat. Nos. 3,298,367; 3,877,428; 4,175,558: 5,019,055; 5,106,374; 5,318,515; 5,348,539; 6,428,505; and 8,257,337 as well as U.S. Patent Application Publication Nos. US 2010/0076413 and US 2012/0267275 and foreign Patent Application Nos. CA 1125134; EP 0217940; EP 0265261; and EP 0462213, for example. Various types of infusion systems for the controlled delivery of therapeutic agents, including some embodiments of the invention, can mitigate or reduce the effect of, or even take advantage of, some or all of these potential problems.
For at least the foregoing reasons, there's a legitimate need for infusion systems for the controlled delivery of therapeutic agents. It would be beneficial and desirable to provide a system that provides an infusion system that improves upon the conventional droplet monitoring technique (described above) and will, therefore, be familiar to and readily accepted by medical practitioners. It would also be advantageous to provide a simple method for the administration of intravenous fluid that is inexpensive to manufacture. Furthermore, it would be particularly helpful to provide an infusion system that permits the user to quickly begin a constant and/or predetermined flow rate in accordance with a prescribed therapy without the need to mix drugs, perform dosage calculations, or adjust the flow rate. It would also be advantageous, particularly for battlefield medicine, remote medicine, third-world health care and natural disaster situations, to provide an infusion system that does not rely on electricity or batteries to power the delivery infused drugs. Providing a self-contained, pre-packaged, sterilized kit containing an infusion system for the administration of drugs and/or fluids, would also offer convenient advantages.